This research concerns the course of development of auditory processing in brainstem centers and the susceptibility of this development to changes induced by manipulations of the early sound environment. Rats serve as experimental subjects for acute unit recording at the cochlear nucleus and inferior colliculus. Manipulation of the auditory history of individual animals includes deprivation and controlled exposure to experimental sound environments. The objective is to characterize the neural events leading to adult auditory processing and to determine their vulnerability to plausible extremes of sound experience.